Wireless Weather Monitoring

Harnessing the power of Doppler Radar to show you the power of Mother Nature, the Weather Canvas is a wireless weather monitoring system that makes the boring task of getting the day�s weather a more colorful and vibrant experience.

Introduction

The Weather Canvas is a robust outdoor weather monitoring system coupled with an indoor LED display. The outdoor system consists of a microcontroller, temperature sensor, humidity sensor, home-made anemometer, a Hot Wheels radar gun modified to measure precipitation, and a solar panel to measure sunlight and charge the microcontroller�s power source. Once per minute, the system transmits the data it has collected to the indoor microcontroller by a 433 MHz RF signal, where the signal is decoded and the information is displayed as a sequence of five vibrant images on the 8×8 RGB LED matrix. The images chosen by the system depend of the weather conditions transmitted. The indoor system uses pulse width modulation (PWM) to provide millions of potential colors to each pixel, allowing for limitless image possibilities.

High Level Design

Rationale

This project was a combination of several core components we wanted to include. Radio frequency communication seemed like an interesting concept to implement, and we were trying to figure out ways to integrate the Hot Wheels radar gun for a long time. Its ability to detect motion was appealing, and we considered doing an invisible fence that is not painful to pets. The Weather Canvas idea came from browsing the Spark Fun website, where we saw an 8×8 RGB LED matrix, and we wanted our project to use it after watching some YouTube videos. Our shared interest in renewable energy led us to solar power, and these ingredients came together for the perfect recipe: a weather monitoring system. After we had decided on the concept, all of the pieces started falling into place: RF to communicate with an indoor unit using the RGB LED display, radar to measure rainfall, and solar power to measure and harness sunlight. The temperature, humidity, and wind sensors followed naturally. We knew integrating these several separate parts would be a challenge but were willing to undertake it to see the final result.

Logical Structure

The most important feature of this project is the RF communication between the outdoor and indoor unit. Without it, the LED matrix would have nothing to display and the outdoor monitoring unit would keep the information for itself. The data path starts at the sensors, whose information is collected by the outdoor MCU. It relays this information indoors with the RF encoder/transmitter. The receiver/decoder unpacks the data for the indoor MCU, which then determines the images to display on the LED matrix based on the data it is has received.

Hardware/Software Tradeoffs

Early in our project design, we had to decide how to implement RF. Our first instinct was to replicate the system used by Meghan Desai in her Wireless Telemetry project. We had allotted the price of the RCT-433 transmitter and RCR-433 receiver and were preparing to write all the encoding/decoding code, which appeared intimidating. Bruce Land made a comment as an addendum to his talk about RF regarding an integrated circuit by Holtek which encapsulates the encoding and transmitting protocols into one hardware unit. After being redirected by several companies including Digikey, we found a supplier at Rentron who was eager to sample us the Linx Technologies RXD-433-KH2 receiver/decoder and TXD-433-KH2 transmitter/encoder modules. The units eliminated the need for software encoding or decoding protocols, solving a software problem in hardware. The fact that they were free made our decision even clearer. One can simply drive the data line with the data to be transmitted, the address line with a unique address (which can be a series of hardcoded ones, zeros or floating) and assert the TE (transmission enable) pin. Any receiver with its address pins configured the same way will have its VT (valid transmission) pin go high and its output data line mirror that of the transmitter.
For more detail: Wireless Weather Monitoring